The present invention relates to an optical add/drop multiplexer (OADM) and a control method therefore. More specifically, the invention relates to an optical add/drop multiplexer with a controlled add amplifier and a method of controlling an add amplifier of an OADM. The invention also relates to an optical add multiplexer (OAM) and a control method therefore.
Wavelength division multiplexing (WDM) is a burgeoning field. The reason so much interest surrounds WDM is the ability to transmit a large amount of information. Each of the wavelengths in a WDM system may carry in excess of 40 Gb/sec and advances in the WDM field are expected to increase the capacity of each wavelength dramatically. Moreover, the number of channels or operating wavelengths is also expected to increase dramatically.
One of the common problems faced by WDM systems and the vendors making WDM equipment is spectral flatness. A spectrally flat signal in which all of the channels have substantially the same gain is preferred because such a signal may be transmitted a longer distance without regeneration while still permitting the constituent channels to be distinguished from one another by a receiver.
To that end, WDM equipment vendors have invested large sums inventing gain-flattened optical amplifiers designed to impart substantially equal gain to signals over the operating wavelength range.
As recognized by the inventors, however, problems occur when an OADM (optical add drop multiplexer) is used to add and drop channels. Specifically, the power balance may be significantly affected when channels are added or dropped and added to a WDM signal.
One method of achieving the desired power balance for a WDM system with an OADM is disclosed in U.S. Pat. No. 6,069,719 (the Mizrahi patent). In that patent, a optical amplifier is placed before or after the OADM to balance or adjust the power levels of the WDM signal.